1. Field of the Invention
The present general inventive concept relates to a frame rate conversion system, and more particularly, to a motion compensated interpolating method of adaptively generating a frame to be obtained by interpolating two frames according to features of a motion vector and an apparatus therefor.
2. Description of the Related Art
Commonly, in personal computers (PCs) or high definition televisions (HDTVs), frame rate conversion is performed for compatibility of programs with various broadcast signal standards such as PAL or NTSC. The frame rate conversion indicates that the number of frames output per second is converted. In particular, in a case where a frame rate increases, a process of interpolating new frames is necessary. Meanwhile, lately, the frame rate conversion is performed after image data is compressed using an image compression method such as a moving picture experts group (MPEG) standard or H.263. In image processing methods, since the autocorrelation of most image signals is great, they contain a large amount of redundancy. Therefore, a data compression effect can be improved by removing redundancy when data compression is performed. To efficiently compress video frames that change with respect to time, it is necessary to remove temporal redundancy. That is, by substituting a motionless frame or a frame in which a small motion exists with a previous frame, the amount of data to be transmitted can be dramatically reduced. Motion estimation (ME) involves looking for most similar blocks between a previous frame and a current frame. A motion vector (MV) indicates how far a block is moved by the ME.
In general, an ME method uses a block matching algorithm (BMA) that considers motion accuracy, real-time processing possibility, and hardware realization. A frame inserted between two frames is mainly generated using the BMA. FIG. 1 is a diagram illustrating an interpolating method suitable for compensating for a motion between frames using the BMA.
Referring to FIG. 1, if pixel values of blocks B included in a frame Fn, a frame Fn−1, and a frame Fi are called fn, fn−1, and fi, respectively, and a coordinate value belonging to the frame Fn is x, an image signal to be obtained by interpolation using motion compensation can be represented as Equation 1.fi(x+MV(x)/2)={fn(x)+fn−1(x+MV(x))}/2   [Equation 1]
However, between the frame Fn and the frame Fn−1, the shape or size of an object is modified by a horizontal, perpendicular, rotational, magnifying, or reducing movement of the object, or the object often disappears or appears. Therefore, since there is a high possibility that images in two blocks matched by the BMA are different, there is a high possibility that a distortion or a blurring effect is generated in the image signal obtained by the Equation 1.
To resolve the above problem, pixel values to be obtained by interpolating the two frames is determined using either the block included in the frame Fn or the block included in the frame Fn−1 as shown in Equation 2. However, in an interpolating method using Equation 2, it is not clear which one of the blocks included in the frame Fn and the frame Fn−1is used.fi(x+MV(x)/2)=fn(x) or fn−1(x+MV(x))   [Equation 2]
Also, when the ME is performed using two adjacent frames, a covered region and an uncovered region appear in a boundary between a background and a moving object. At this time, if the ME is performed in only one direction between the two frames, a hole and an overlap are generated in a frame to be obtained by interpolation due to the covered region. Therefore, in order to prevent the hole and the overlap from being generated, the frame Fi to be obtained by interpolation is generated using bi-directional ME. However, since a motion must be estimated in two directions in the bi-directional ME method, an amount of computation increases and a volume of hardware also increases.